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length where longest, directed obliquely forwards, and diminish in 

 size as they approach the extremity of the tail. In Cook's Phalan- 

 ger I find the hcemapojjhyses commence between the second and third 

 caudal vertebrse, increase in length to the fourth, and then pro- 

 gressively diminish to the end of the tail : the penultimate and an- 

 tepenultimate presenting a permanent separation of the lateral moie- 

 ties, and an absence of the spine. 



" In the Potoroos the extremity of the long anterior spines is di- 

 lated, and produced backwards and forwards ; the posterior smaller 

 ones become expanded laterally, and give oflF similar but shorter pro- 

 cesses from each side, whereby the base of the support is extended. 



" In the Great Kangaroo the spine of the first subvertebral arch 

 only is simple and elongated ; the extremities of the others are ex- 

 panded, and in some jut out into four obtuse processes, two at the 

 sides and two at the interior and posterior surfaces. In a carefully 

 prepared skeleton of Macropus Benettii, I found these inferior spines 

 wanting between the last nine vertebrae of the tail. In the Petau- 

 rists, Phascogales, and Dasyures, where the tail acts as a balancing 

 pole, or serves, from the long and thick hair with which it is 

 clothed, as a portable blanket to keep the nose and extremities 

 warm during sleep, the subvertebral arclies are also present, but 

 less in number, and of smaller relative size. They are here princi- 

 pally subservient to the attachment of muscles, — their mere mecha- 

 nical office of defending the caudal vessels from pressure not being 

 required. 



" The ribs consist of thirteen pairs, excepting in the Wombat and 

 Petaurists : the first of these is the shortest, and, except in some of 

 the Petaurists, the broadest. In the Pet. macriirus, the fifth, sixth, 

 or seventh are the broadest, and the ribs generally have, both in this 

 species and in Pet. scmreus, a more compressed form than in the 

 other Marsupials ; but this character docs not exist in Petaurus 

 Taguanoides. In the Great Kangaroo they are very slender and 

 rounded, except at the sternal extremities, which are flattened for 

 the attachment of the cartilages. In this sj)ecies the anterior pairs of 

 ribs articulate directly with the sternum. The cartilages of the other 

 jiairs are long and bent towards the sternum, but do not join it ; nor 

 are they confluent, but have a gliding motion one over the other. 

 In the Opossum there are seven pairs of true ribs, and six which 

 may be regarded as costa notha. In the Wombat six pairs only out 

 of the fifteen reach the sternum. 



"The sternum consists of a succession of elongated bones, gene- 

 rally six in number, but in the Wombat four. The first bone, or 

 manubrium, sterni, is the largest, and presents in many species a tri- 

 angular shape, from the expansion of its anterior part, and some- 

 times a rhoraboidal figure. A strong keel or longitudinal process 

 is given off in many species from the middle of its inferior or outer 

 surface ; the side next the cavity of the chest is smooth and slightly 

 concave. In the Wombat, Phalangers, and others, the keel is pro- 

 duced anteriorly into a strong process, against the sides of which 

 the clavicles abut : the first i)air of ribs join the produced anterior 



